Image acquisition, correlation and detailed visual inspection of component in periodic motion

ABSTRACT

Embodiments disclosed herein include, but are not limited to, methods for capturing video sampling data comprising a plurality of video images of a moving object, for example using one or more cameras positioned on a stationary frame of reference adjacent to the mechanical component under investigation, in which a change in motion of the moving object is correlated to an origin frame obtained from the sampling data and representing a point at which the change in motion first occurs.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of, and claims benefit ofand priority to, U.S. Nonprovisional Utility application Ser. No.16/777,228, filed Jan. 30, 2020, itself a continuation-in-partapplication of, and claiming benefit of priority to, U.S. NonprovisionalUtility application Ser. No. 16/748,065, filed Jan. 21, 2020, which isnow patented as U.S. Pat. No. 10,762,639 having an issue date of Sep. 1,2020 and claiming the benefit of priority to U.S. ProvisionalApplication No. 62/795,189 filed on Jan. 22, 2019, the contents of eachof which are fully incorporated herein by reference.

FIELD OF INVENTION

The present embodiments pertain to systems, apparatuses, and methods foranalyzing movements in machinery, machine components, and inanimatephysical structures; processing of visual data related to suchmovements; and visual inspection of moving components by reconstructingvideo images that have enhanced frequency or angular resolution thancould be achieved without the use of digital photography.

BACKGROUND

All machines and physical structures produce vibrations and resonancesof various kinds, some of which may be characteristic of normaloperation and others of which may indicate off-normal conditions,unusual wear, incipient failure, or other problems. In the field ofpredictive maintenance, the detection of vibrational signatures is a keyelement of the diagnostic process in which the goal is to identify andremedy incipient problems before a more serious event such as breakdown,failure, or service interruption occurs. Often it is desirable tovisually inspect a mechanical component to determine if physical damageis present. This can be done by stopping the motion and performing aphysical inspection; however, shutting equipment down and interruptingits operation to determine the presence of a fault condition or theextent of damage is undesirable.

One method that has been used to perform visual inspections while amachine is still in operation is by means of a stroboscope. Thisinstrument flashes a high intensity light at user selected frequencies.When the frequency of flashing is exactly at the frequency of interest,the motion of the moving component appears to freeze. When the frequencyof flashing differs slightly from the frequency of motion, then thecomponent will appear to turn very slowly in a forward or backwarddirection. However, the stroboscope is limited by the perception of thehuman eye. Very slow frequencies are too intermittent to give aperception of stopping the motion because there is too large of a delaybetween the flashes. At very high frequencies, the flashes are so closetogether that the eye only sees a steady source of light and thisprevents the motion from appearing to be frozen.

Since digitally captured data can be played back at any frequency whichsuits the perception capabilities of the human eye, it allows very slowor very fast frequencies to be rendered in a visually perceptive manner.Additionally, by selecting sample rates which are not synchronous withthe frequency of interest, reconstructed video output can render whatappears to be a very high angular resolution of the component whichwould normally only be achievable by cameras with a very high framerate. When the frequency of interest is too high to be adequatelycharacterized satisfactorily by the frame rate of the camera, thedigital phenomena of aliasing still allows a video stream to beconstructed that provides a very high detail examination of thecomponent as it progresses through its cycle.

Also, whereas a stroboscope depends on the skill of the user to locatethe correct frequency of motion and then to make the component turnslowly, by comparison a more preferred video system would only requirethe user to identify the object of interest by making a graphicalselection from a single frame of the video. The system couldautomatically, and without variability that depends on user actions,determine the frequency of motion, calculate an optimum frame rate, setthe shutter rate to the maximum or equivalently sets the brightnesscontrol or exposure time to the minimum value or sufficiently smallenough value, collect the needed data, and reconstruct an output videowhich would enable a visual inspection of the component with very highresolution. Current embodiments are directed to providing this advantagewith digital photography and video.

U.S. Pub. No. 2016/0217587 titled “Apparatus and Method for AnalyzingPeriodic Motions in Machinery” (Hay, Jeffrey R.; published Jul. 28,2016), and later issued as U.S. Pat. No. 10,459,615, the contents ofwhich are incorporated by reference herein, describes multipleembodiments that provide a non-contact vibration analysis system formachinery and structures. The embodiments described therein provide anumber of features and advantages, not least among them is a flexiblepredictive maintenance tool that use vibrations to diagnose faultconditions using a video-based tool for evaluating the dynamic motionsin machinery without the need for edge visualization or identificationof other specific objects in the scene.

For example, the descriptions contained in US Pub. No. 2016/0217587refer to multiple embodiments of a system for analyzing periodic (i.e.,repeated) motions in machinery. This system comprises one or more videoacquisition devices, such as but not limited to a video camera,positioned at a selected distance from a machine component or physicalstructure (i.e., object). This video acquisition device will bepositioned with an unobstructed view of a selected portion of the objectto obtain a video feed. This video, as is the case with the videosdescribed in the present disclosure, is divisible into individual imageframes, with each frame showing a static image of a scene, and with eachframe being divisible into a plurality of pixels. This system furthercomprises a data analysis system, including a processor and memory toanalyze the video file, such as by measuring a value which ischaracteristic of the object's physical movement over time to therebydetermine the periodicity of that movement. The system in U.S. Pub. No.2016/0217587 further comprises a data storage system to archive thevideo for later retrieval and comparison of the images and themeasurements from the video, the image frames, or an enhanced version ofthe video. This comparison is the foundation for providing determiningchanges in the object's movement data, which may be indicative ofmechanical anomalies.

In any such endeavor, however, it is important to understand thatcertain movements of interest by an object happen at such a highfrequency as to not be discernible by a human observer with the nakedeye or a person watching a video obtained from an actual scene withmoving parts. For example, a vibration occurring in a machine componentat 60 Hz, as an example, may need to be slowed down on video to discernwhat is actually happening with the component. With appropriate programinstructions, the inventive system and methods disclosed herein may thenbe configured to compare spectrums for the two videos to see what peaksare shared. The shared peaks could be counted as normal behavior,whereas the peaks that are not common to the two spectra may beidentified as changes in the vibration behavior, which may be associatedwith deteriorating conditions. Such approaches make the practice of thepresent embodiments more efficient and less prone to guess work.

Often, the conditions that indicate a problem or need for interventionthat are captured by the video acquisition device are subtle ones thatoccur simultaneously with normal movements (i.e., substantially asdesigned and not a root cause or indicator of ongoing or futureproblems) of a machine or component. Consider a shaft that rotates as anormal movement, yet also has a vibration undiscernible to the naked eyethat is accompanying this rotational movement. In this sense, the normalrotation of the shaft is not of concern, but one investigating thecondition of the shaft would be interested in waveforms of each rotationfrom which the vibrational anomaly can be determined. Examples wherevisual inspection might be very helpful would include damaged or dirtyblades, bent, bowed, or damaged shafts, and looseness or rubs.Accordingly, as discussed herein, the present embodiments efficientlyand reliably achieve the objective of verifying specific faultconditions clearly based on a visual inspection based on recorded imagesacquired while the component is in normal operation.

In some settings, it likewise is beneficial to have an external triggerthat can be used to control the acquisition of images with a camera toenable visualization and measurement of motions. The benefits includemore precise imagery and reduced requirement for obtaining imagesmanually.

SUMMARY

In an embodiment, after a user sets up a digital video camera to viewthe mechanical structure of interest, identifies the mechanicalcomponent to be inspected graphically from the image of the mechanicalstructure, the system identifies the dominant frequency of the componentto be inspected (e.g., the periodic movement of a drive shaft), sets adesired frame rate, sets the shutter rate to the maximum or equivalentlysets the brightness control or exposure time to the minimum value orsufficiently small enough value, and captures a video of minimumduration. As desired, a lighting check may be employed to recommend theneed for additional external lighting. As described more fully herein,some embodiments provide a desirable feature through the use of multiplefrequency spectra, in which a system automatically sets an acceptablesampling rate and duration to achieve the desired angular resolutionbased on the frequency of the periodic motion and the frame ratesavailable in the camera, and the system automatically incorporates theuse of aliasing as needed to obtain the optimum reconstructed video.Moreover, the system can be programmed so a user can override theautomated selections as desired. Once the reconstructed video isavailable, the user can stop the motion playback of the mechanicalcomponent or slowly rotate through its periodic cycle to visuallyinspect all surfaces. As desired or needed, the original video can bestabilized to remove camera motion or filtered to remove otherdistracting motion. The reconstructed video can be played back atdifferent rates and the motion can be looped and amplified to allowvisualization of small motions such as shaft runout.

In one aspect of the inventive system and method, consider a shaftrotating or reciprocating at 30 Hz (30 repetitions every second). If theframe rate of the video camera is set at 30 frames per second, it wouldtake one sample from each cycle of rotation or reciprocation at exactlythe same angular or linear position on the shaft. If the video wereplayed back to the user, the shaft would not appear to be moving. Inorder to prevent the 30 Hz frequency from aliasing in the recorded imagethe frame rate of the camera must be greater than two times thefrequency of interest, in this case greater than 60 frames per second.

Now consider the situation that occurs if the video is recorded at 30.1frames per second. The video frame captured at each rotation is at aslightly different angular location on the 30 Hz periodic motion ofinterest. During steady state operation, each frame captures the motionof the component at a slightly different angular location along themotion waveform. After collecting 10 seconds of data, 301 cycles of the30 Hz motion are captured; and the full 360 degrees of the periodicwaveform will be captured with a resolution of 300 samples (1.2 degreesof angular resolution). Without using the aliasing effect, this resultwould require a camera able to record with a frame rate of 9000 framesper second to achieve this result. But with present embodiments, oncethe video is captured and properly reconstructed, the component can beslowly rotated backward or forward through its motion to visuallyexamine the component under the control of the user. This data may needto be filtered to remove motion that may be present at otherfrequencies, or to remove or normalize uneven illumination over theduration of the frames. Whether data is collected from applications withlow frequencies of interest, for example less than 120 revolutions perminute (2 Hz) or from high frequencies, for example greater than 5400revolutions per minute (90 Hz), this method will enable detailedevaluation of a single cycle of the motion of the component.

Accordingly, the result provides a high phase resolution even though thevideo camera used to acquire it has a limited frame rate, along with amodified playback rate adapted for improved visual inspection. Stateddifferently, the naked eye would not detect all the features when asingle cycle happens in the span of 0.5 sec (30 Hz) with as muchprecision as if the cycle were slowed down to 150 seconds. In thisregard, the limitations of the video camera operating at 30 frames persecond approximate the same limitations of the human eye. However, eventhough acquired at a rate of 30 frames per second, aliased frequencyenables playback to be slowed down so that very small features on theobject being inspected can be discerned.

Additionally, the inventive system and method provide corollary featuresto assist a user. In some embodiments, a user is able to define an areaof the machine or machine component from which to obtain aliasedfrequencies. This is accomplished by machine-readable programinstructions that allow a user-controlled interface to define a regionof interest on a monitor during video playback, appearing as a boxaround a particular area, portion or component of a machine toinvestigate. Subsequently, movements depicted in video as occurring inthis region of interest are then processed as described herein. Examplesof processing discussed in further detail herein include, withoutlimitation, amplifying the movements in the video by differencing framesobtained in the video at two different times and multiplying theamplitude differences in those frames by a predetermined factor,rescaling, filtering out all frequencies except a subset of thosefrequencies identified in the region of interest from a frequencyspectrum plot, or resampling the movement as an aliased frequency (e.g.,changing from a sampling frequency of 60 Hz—i.e., 60 frames per second(“fps”)—to a lower frequency such as 30 Hz). An example of thesefeatures to enhance the visual depictions in the processed video isfound in US Pub. No. 2016/0300341 titled “Apparatus and Method forVisualizing Periodic Motions in Mechanical Components” (Hay, Jeffrey R.et al.; published Oct. 13, 2016), the contents of which are incorporatedby reference herein. This application, now patented as U.S. Pat. No.10,062,411, describes multiple embodiments in which a new image sequenceor sequences are computed, showing the movements of an object(s) inmotion being visually amplified.

Other options and alternatives within the scope of these embodimentsinclude machine-readable program instructions that operably control aslider bar or a circular dial allowing a user to rotate the orientationof the shaft being evaluated in the video. For example, a first positionon the slider bar (e.g., to the far left if the slider bar ishorizontal, or at the bottom if the slider bar is vertical) might beused to indicate the absolute position of the shaft at origin. Fromthere, a second, user-selectable position on the slider bar would matcha position of the shaft at any given point in its cycle as shown in thevideo based on the movement over time, represented by the secondposition on the slider bar. As an alternative to a slider bar, one mightconfigure a circular dial controllable by a user for selecting the pointof the cycle that will be shown, where a point on the dial is designatedas absolute position (i.e., beginning point in a cycle) and the numberof degrees the dial is turned may reflect the progress of the objectwithin its cycle of motion. Furthermore, this phase control mechanismcan be manipulated by a user for positioning of the shaft or otherobject being evaluated during playback, for example to focus upon aparticular moment of movement being evaluated at a certain point alongthe timeline. This in turn would be used to provide phase indicationcharacteristics relative to the position of the shaft at particulartimes in the video.

Various embodiments disclosed herein may utilize different methods forcapturing video sampling data comprising a plurality of video images ofa moving object. In many cases, the cameras will be positioned on astationary frame of reference adjacent to the mechanical component underinvestigation. However, other embodiments may utilize a camera attachedto a drone in order to get video from the proper angle or from multipleunits in an application such as a wind turbine farm. In such embodimentsthe data may require stabilization processing to remove the motionassociated with the drone. Sometimes this also is necessary forstationary applications because of floor motion produced by nearbyequipment in a facility.

In still other embodiments, an internal clock on the camera, a timedpulse, or an external trigger are used for image acquisition. For imageacquisition according to the latter approach, an external trigger allowscontrol over the camera to acquire the images, allowing for improvedvisualization and measurement of motions. As one example, a lasertachometer may be used as the input. The tachometer is connected to andin communication with the camera and configured so that when it sensesan external stimulus upon the component of interest, it sends a pulse tothe camera as a command to take an image. An external stimulus that issensed and which acts as this trigger can be selected from a range ofoptions known in the art, including items such as reflective tape or akeyway the tachometer is programmed to identify. When such a systemobtains a series of images (one image per revolution), a video of thecaptured motion can be created. This video will show any motion that isa result of any component not coming back to its same position. A fanblade that comes back to the same position in each rotation or arotating or reciprocating shaft are examples of components on whichthese embodiments can be used. With a fan blade, as one example, a lasertachometer may be positioned to sense the blade arriving at the originalposition, which sends a pulse to the camera to acquire a series ofimages with the blade in the same orientation. In still furtherembodiments, images are enhanced such as by detecting and amplifying orenlarging vibratory movements and other motion to visualize all themotion present as a result of components not coming back to theiroriginal locations.

BRIEF DESCRIPTION OF DRAWINGS

The patent or application file with respect to the present disclosurecontains at least one drawing executed in color. Copies of this patentor patent application publication with color drawing(s) will be providedby the Office upon request and payment of the necessary fee.

The drawings, schematics, figures, and descriptions contained in thisapplication are to be understood as illustrative of steps, structures,features and aspects of the present embodiments. Accordingly, the scopeof embodiments is not limited to features, dimensions, scales, andarrangements shown in the figures.

FIG. 1 is a graph that shows a periodic waveform from a repeated cycleof movement of a moving object, having been obtained exactly at thefrequency of repetition, and representing collected sampling datasampled from the same position in each cycle of the waveform, in whichthe sampled data may be collected by capturing visual images digitally.

FIG. 2 is a graph that shows the periodic waveform out of phase with thefrequency of a repeated cycle of movement of the moving object, andrepresents collected data sampled from different positions in thewaveform cycle, according to multiple embodiments and alternatives.

FIG. 3A is a graph that shows the periodic waveform likewise out ofphase with the frequency of a repeated cycle of movement of the movingobject, and represents collected data sampled from different positionsin the waveform cycle, according to multiple embodiments andalternatives.

FIG. 3B is a reconstructed graph that provides a detailed view of theperiodic waveform from aliased data collected on many cycles of theperiodic motion waveform from FIG. 3A, according to multiple embodimentsand alternatives.

FIGS. 4A-4E offer schematic views representing damage to a tooth on abelt-pulley component at different angular positions, as an illustrationof a condition which can be detected through the practice of multipleembodiments and alternatives described herein.

FIGS. 5A and 5B are photographs depicting damage to a first ventilationfan and a second ventilation fan, respectively, as an illustration ofconditions which can be detected through the practice of multipleembodiments and alternatives described herein.

FIG. 6 is a single frame from the reconstructed video of a windmill withmultiple damaged blades, as an illustration of a condition which can bedetected through the practice of multiple embodiments and alternativesdescribed herein.

FIGS. 7A and 7B are photographs that offer perspective views of one ormore wind turbines with acquisition of video images collected withdrones, according to multiple embodiments and alternatives describedherein.

FIG. 8 is a photograph of a blade with ice accumulation on the turbineblades that would be very difficult to evaluate in operation, yetvisible with reconstructed video images that enable more detailed visualinspection during normal turbine operation, in accordance with multipleembodiments and alternatives described herein.

FIG. 9A and FIG. 9B provide an illustration of an aliasing effectresulting from digital data captured at different sampling rates,according to multiple embodiments and alternatives.

FIG. 10 is a photograph of a rotating shaft with reflective tape,associated with illustrating an example use of multiple embodiments andalternatives.

FIG. 11 is a photograph of a rotating shaft with setscrews serving asmarkings and designated as right and left areas, associated withillustrating an example use of multiple embodiments and alternatives.

FIG. 12 is a photograph of a fan blade with an area marked withreflective tape, associated with illustrating an example use of multipleembodiments and alternatives.

FIGS. 13A-C provide a schematic illustration of markings upon a unitsuch as the one shown in FIG. 11, associated with illustrating anexample use of multiple embodiments and alternatives.

MULTIPLE EMBODIMENTS AND ALTERNATIVES

Embodiments described herein provide an improved manner of diagnosingthe conditions of machinery and other moving objects by the detection ofvibrational signatures. The detailed evaluation of a cycle of motion forsuch objects is able to approximate the resolution that would beobtained with much more expensive equipment marked by a frame rateacquisition capability that is unavailable in most commerciallyavailable cameras or very expensive and largely cost prohibitive wheresuch capability might exist. The following descriptions are directed tothe main aspects of this novel capability as well as corollary featuresthat include, without limitation, the capability to focus on a specificregion of interest depicted in the frame, freeze its motion or track itwith very high definition through it cycle of repetition and,optionally, other processing enhancements such as detecting andamplifying vibratory or other movements, filter frequency, phaseindicators, and control of the object's placement within a cycle ofmotion.

In an exemplary embodiment, a system is provided which evaluates amoving object undergoing periodic motion, with the use of at least onevideo acquisition device (e.g., video camera) that acquires video imagesof the moving object. The frame rate on the video camera can beadjusted, allowing video images to be acquired at a frequency that isasynchronous with the frequency of movement of the object as itundergoes periodic motion, i.e., cycles of motion that can bereciprocating, rotational, elliptical, parabolic, and so forth. Thesampling rate may not be fast enough to prevent the frequency ofinterest from appearing in the data as an aliased frequency and in thiscase, the acquisition rate is normally set slightly higher or lower thanthe frequency of interest so that one sample per cycle of motion isacquired. Alternatively, faster sampling rates (about twice thefrequency of interest, for example) also can be used which will resultin multiple samples being acquired on each cycle of repetition andreducing the total acquisition time required. The system furthercomprises a processor and a memory, the latter for storing images thatare acquired and modified, and the former for operating a computerprogram suitable that executes a number of computer functions describedherein. In some embodiments, the computer program operates to isolatevideo image frames collected over multiple cycles and reconfigure thoseinto a modified video that represents one cycle of motion. Each of thevideo image frames represents a portion of the source videocorresponding to a specific position in the cycle of movement of theobject.

Aliased Slow Mode Acquisition

In some embodiments of the present disclosure, system features describedherein enable a user to select a frame rate that is asynchronous with afrequency of interest. For example, consider a shaft that normallyrotates at 20 Hz (20 cycles per second). The user may set the frame rateto 20.1 Hz, and the data that is acquired includes an aliased frequencyof 0.1 Hz as a subset of the 20 Hz motion. Through a series of aliasedfrequencies obtained in this way, a user collects data to characterizethe 20 Hz motion in a motion amplified data set. Although the actualtime to complete a cycle takes 0.05 seconds, the system would need tocollect 360 cycles of data to achieve a one-degree resolution in thereconstructed video. This would require the system to collect 18 secondsworth of data. The reconstructed video produced according to presentembodiments would present one cycle of the shaft, or loop this cycle, atany playback speed which facilitates visual inspection includingindividual frames at any selected angle in the shaft rotation.Additionally, in some embodiments the system will have stabilized theoriginal video to remove camera motion, filtered the video to removefrequencies not of interest to this inspection, or amplify the motionpresent in the shaft to allow the motion to be perceptible to the humaneye. In some embodiments, the system is configured so a user can selectone or more spatial regions where amplification is to occur, oralternatively where amplification is to be suppressed while thenon-selected region is amplified.

In order to capture this data without the aid of the aliasing phenomenadescribed herein, the camera would have needed to sample the shaft at7200 frames per second. This frame rate is well above what is availablefor most cameras that are suitable for use in industrial applicationsand, if such high-performance cameras were available, they would addsignificant cost to the inspection system. As described herein, wheninspecting mechanical components with a high frequency of periodicmotion, a complete cycle with high angular resolution could not bereconstructed without the use of the aliased frequencies. In this case,a user may filter captured video data to only include frequencies veryclose to 0.1 Hz in order to present the movement at these aliasedfrequencies without any contribution from other frequencies.

FIG. 1 illustrates the result of sampling a periodic waveform (graphingthe amplitude of motion in repeated cycles) of a moving object exactlyat the frequency of repetition of the mechanical component underinvestigation. Sampling the periodic waveform at some integer multipleof the frequency of repetition creates the same effect. In thiscircumstance, each sample is collected from the same position(s) in eachcycle of the waveform. No matter how video frames data are acquired, thesame angular positions are sampled from each cycle and no newinformation is gained by sampling multiple cycles of the mechanicalcomponent. FIG. 2 and FIG. 3A show the effect of sampling a periodicwaveform asynchronously to the frequency of repetition. In this case,samples are acquired from different angular position(s) in each cycle ofthe waveform. In this case, the video frames captured from each cycleprovides new information about the mechanical component. FIG. 3B, agraph extracted from a periodic waveform obtained by under-sampling inwhich the aliased frequencies were collected at a frequency differentfrom the frequency by which the component completes each cycle,illustrates how the samples from multiple cycles can be repositionedinto one cycle with greater angular detail. The same principles wouldalso apply for a reciprocating object or piece of machinery as it cyclesthrough its motions. Similarly, the video frames captured asynchronouslyto the periodic motion being investigated can be reconstructed into avideo providing extremely high angular resolution of the mechanicalcomponent as it goes through one cycle of motion. This method ofreconstructing a video sequence allows visual inspections to beperformed without disrupting the operation of the machine which wouldotherwise not be possible.

An exemplary use of the inventive method may be as part of a shaftinspection tool. As frames are reconstructed and recombined from manycycles of operation, the video will display greater angular detail asmore cycles of video are recorded. Previously, an example was describedof a 0.1 Hz aliased frequency, but many other aliased frequencies arewell within the scope of present embodiments. In all cases, theresulting video will enable the user to present a complete high phaseresolution video of one or more periods of the motion of the mechanicalcomponent despite any limitations with respect to the frame rate of thecamera as compared to the frequency of the periodic motion to beexamined.

Other uses of the inventive aspects described herein are shown inseveral figures. For example, FIGS. 4A-E illustrate how this approachcould be used to investigate a belt-pulley system on a machine. In thesefigures, a missing tooth from the belt is very apparent at locationswhen the belt is not in contact with a pulley wheel. Although for allpractical purposes the belt cannot be inspected while the machine is inoperation due to the speed of operation, the video inspection systemdescribed in these embodiments could, as further described hereinisolate the frequency of the belt as distinguished from the rotationalfrequency of each sheave pulley; select an appropriate sampling rate foranalyzing the belt; and acquire an appropriate number of cycles ofrotation. The reconstructed video could then freeze the motion of thebelt, or loop one cycle of the belt rotation repeatedly at the measuredamplitudes or with the motion amplified at any playback speed selectedby the user. In addition, the motion can be frozen, and the user canselect views at any angular location in order to do a detailed visualinspection of the belt.

In FIGS. 5A and 5B, the ventilation fans have experienced damage thatcould not be seen with the fans in operation. FIG. 5A depicts a fan in afrozen condition where the damage due to rust can be seen on the bladearound the angular position of 90 degrees (3:00 on a clock face)although partially obscured by a support structure, and FIG. 5B depictsthe fan in a damaged condition in which the eroded blade is easilyvisible as noted by a circle near angular position zero degrees (12:00on a clock face). Such are examples of conditions that can be detectedand analyzed by the practice of embodiments provided herein.

Likewise, FIG. 6 is a single frame from the reconstructed video of awindmill with multiple damaged blades. Again, this illustrates acondition which can be detected through the practice of presentembodiments. Even though the presence of some damage could be seen whenthe windmill was turning at slow speeds, the full extent of the damagecould not be assessed during operation to the extent provided throughthe practice of the present embodiments. In like manner, conditionsassociated with the wind turbines in FIGS. 7A-7B and the iceaccumulation on the blade in FIG. 8 can be evaluated and diagnosed priorto failure, using the systems and methods herein. Although the cameramay need to be mounted on a drone to gain an advantageous perspective ofthe wind turbine, the ability to perform detailed blade inspectionsduring normal operations could not be accomplished without the use ofembodiments such as those described herein.

In some embodiments, a user may select a low exposure time to limit theamount of motion blur. The system may do this automatically. The systemmay adjust the settings of the camera automatically so that they areappropriate for inspecting a shaft requiring a small exposure time. Thesystem may automatically determine the speed of the shaft, andautomatically set the frame rate of the camera appropriately so that itis slightly off the rate of the shaft to produce the aliased frequencyas discussed herein. In the above example, once the of 20 Hz motion ofinterest has been specified or measured by any means known in the art,the system will automatically select a frame rate of the camera, or thiscan be set by the user to a value suitable for producing an aliasedfrequency, such as 20.1 fps to produce a 0.1 Hz aliased frequency, or a30.2 fps to produce a 0.2 Hz aliased frequency, as non-limitingexamples. The signal could also be sampled asynchronously at frame rateof 100.1 Hz without aliasing and capture 5 points on each period of the20 Hz signal of interest. In this case, the system would only need tocollect about 3.5 seconds or 72 cycles of data to achieve one degree ofangular resolution. The faster sampling rate works well and reduces dataacquisition time if the system is operating in a very stable manner butgives less satisfactory results if there is some variation from cycle tocycle of operation.

While present embodiments are not limited to any specific sampling rate,in some cases a sampling rate may depend on and be determined by userpreference for resolution between image frames being acquired andrepositioned in a reconstructed (i.e., modified) video. For example,“Freq” means the frequency of a given periodic motion of interestexpressed in Hz; “N” means a number of samples to acquire per cycle ofmotion; “Resolution” refers to a desired angular resolution in areconstructed period of motion of an object expressed in degrees; “ΔRev”defines the resolution expressed as a fraction of a revolution. With theforegoing meanings, the equations for determining a sampling rate,SampleRate, expressed in units of frames per second are given below:ΔRev=Resolution/360SampleRate=N*Freq*(1+ΔRev)

The value of N could be established by the user or set automatically bythe processor to obtain the highest possible sampling rate availablefrom the camera and minimize the total sampling interval required toachieve the specified resolution in the reconstructed cycle ofrepetition.

FIGS. 9A-B and Table 1 below illustrate the phenomena of aliasing whichoccurs when sampling data. Here, the aliasing effect results fromdigital data captured at different sampling rates. Aliasing is generallyprevented when digitally processing signals by applying analog filtersto remove the higher frequencies that would be aliased, to prevent thesefrequencies from being folded into the lower frequency data. An equationwhich can be used to determine location of the aliased frequency intothe range of the digitally sampled data is FR=TF/F_(max), where TF isthe true frequency, FR is the frequency ratio, and F_(max) is themaximum frequency in the frequency spectrum such that F_(max)=0.5 timesthe Sample Rate (or Frame Rate).

When the form of FR is viewed as a whole number (N) plus a fraction(Frac), FR=N·Frac, then the aliased frequency (AF) can be calculatedusing the following formulas:If N is Odd, then AF=Fmax−Frac*FmaxIf N is even, then AF=Frac*Fmax

By way of further exemplary illustration, Table 1 provides the differentaliased frequencies which occur for a sine wave of 384 Hz when sampledat less than two times this value.

TABLE 1 Table of aliased frequencies when measuring a 384 Hz motion ofinterest resulting from various frame rates: Frames per F_(max)Frequency Aliased second (Hz) Frequency (Hz) 100 50 16.0 120 60 24.0 200100 16.0 300 150 84.0 400 200 16.5 500 250 116.5Reconstruction of Frames

In some embodiments, a user selects a frame rate slightly off from theperiodic motion of a machine or component undergoing movement at afrequency of interest. That sampling frequency may be asynchronous (outof phase) with the vibration or motion of interest. To illustrate innon-limiting fashion, the frame rate might be 3% higher or lower thanthe actual frequency of rotation. For example, if the machine has ashaft rotating at 30 Hz, the camera may record images at 30.1 frames persecond, or “fps” (30.1 Hz), referred to herein as an aliased samplingrate (ASR) frequency. An ASR frequency may be selected by a user, orautomatically set by the system. An ASR frequency may be greater or lessthan the actual frequency of the moving object. For example, in someembodiments, an ASR frequency which is 1 Hz or less different than theactual frequency of the moving object may be suitable. At higherfrequencies, a difference of 10 Hz may also be suitable, or in somecases the difference between an ASR frequency and the actual frequencymay be in tenths of a Hz. The result is the camera will sample differentlocations on the rotating or reciprocating component; this results inthe sampling of different positions on the waveforms for each cycle, asillustrated in FIG. 2. This may be used to sample frequencies muchhigher than can normally be achieved by the camera. This method may bebeneficial when the machine is operating at a steady state and themotion of the machine component or vibration do not change.

The fact that the camera keeps sampling at different angular positionsof the periodic signal will allow the software to capture enough imagesover time that each angular position of the periodic signal can berepresented in the video, as illustrated in FIGS. 3A-B. In this manner,a camera may acquire data for a sufficient time to reconstruct a fullwaveform or periodic event (seen in the video in this case). Forexample, in the first pass of the periodic signal the camera may acquirean image in the periodic signal that represents the 10th degree positionof 360 degrees. Then the next pass at the periodic signal may enable thecamera to capture the 15th degree. This would keep occurring for 72cycles of the motion (360/5=72), then the video is reconstructed to showone periodic signal that is really comprised of images from framesselected from multiple cycles of the signals. This allows the camera toachieve a much higher resolution video as well as faster vibrations thancan normally be achieved by a camera.

As previously noted, various forms of image processing are within thescope of the present embodiments, e.g., amplification or rescaling.Another capability involves recording a moving piece of equipment, forexample a shaft rotating at 30 Hz, to return a high-resolution video ofthe motion with high angular resolution. To further illustrate, in ashaft rotating or reciprocating at 30 Hz, if acquisition was done bysetting the framerate of the camera at 30.1 Hz, one would slowly acquirea series of videos separated by 33.33 milliseconds (1.0/30.1) in time.For the 30 Hz periodic motion of interest, the system could acquirevideo data over 301 cycles in 10 seconds, providing a resolution of 1.2degrees in the single cycle presented in the reconstructed video.Reconstructing the full or substantially full waveform in this mannerwould allow reconstruction of 30 Hz waveforms providing full or nearfull imaging of the motion in the scene.

It will be appreciated that the methods described here will result inmany frames, in the video content acquired over many cycles of theperiodic motion of interest. In the previous example, 1 image per cyclewas stored (representing the aliased frequency), but by keeping all theacquired images and assigning them to a particular phase of rotation,such as in the example of a rotating shaft, the system is able toreconstruct one cycle in the appropriate order by filling in gaps of theshaft's position as new images are acquired. Once every phase of therotation is represented (depending on desired resolution), theacquisition can be stopped. Sampled frames are assigned phase valuesbased on the time at which the frames are acquired. If the frequency ofthe periodic motion of interest is known, and the elapsed time foracquiring each frame is known, then the phase position for each frame inits respective cycle of motion can be calculated or determined.

Automatic Frame Rate Determination

A problem that exists with currently available methods is the need forthe user to set the frame rate for capturing the video images. For auser who may lack complete knowledge of signal processing or the currentoperational state of the machine, this may result in under-sampling, aswell as lost efficiency through laborious trial and error as the userattempts to determine an appropriate frame rate on the camera.

Another embodiment which may allow a user with less skill to obtain thedesired results also requires the acquisition of two separate videos. Ina first acquisition, the camera is set to its highest frame rate for thevisual field selected or at least 2.0 times the highest frequency ofinterest. When the frequency for the motion of interest is determined asa result of being selected by the user from a frequency spectrum, thesystem automatically determines the best sampling rate (or a suitablesampling rate) and the collection duration for capturing the secondvideo recording to provide visual inspection of the mechanicalcomponent.

Further, as data about a machine or machine component is gathered, auser may be aided by knowing/determining the frequency of interest aheadof time from some other external measurement such as a tachometer andhaving a steady state condition during acquisition. Accordingly, in someembodiments a user may enter the value of the rate of rotation orreciprocation of the component of interest, and the system automaticallydetermines the best sampling rate (or a suitable sampling rate) and thecollection duration for capturing the video recording to provide visualinspection of the mechanical component with a desired degree of angularresolution.

Control of Image Acquisition

In some embodiments, a device is used to produce a trigger that causesthe camera to obtain each image in a series of images. As a non-limitingexample, a laser tachometer may be used as the input such that itproduces a trigger each time a rotating shaft rotates to the sameangular position the laser sensing a reflective marker or keyway on theshaft. When the laser tachometer senses an external trigger, e.g.reflective tape or keyway, it sends a pulse to the camera which acts asa command to take an image. In this scenario, the rotating shaft willcone back to the same angular orientation in each revolution. In anexemplary use case, the camera is set to a small acquisition time toenable a sharp image. In accordance with the teachings herein, a seriesof images acquired one per revolution can be combined to create a video,which shows motion that is a result of a component of interest notcoming back to its same position. Again, by way of non-limiting example,if all motion is vibration which is harmonically related to the runningspeed, then the rotating element will appear perfectly frozen in a stillposition. However, when other vibrations which are not harmonicallyrelated to the shaft are present, then the shaft will exhibit thismotion. Mathematically this motion can be submitted to one or moreadditional processes that amplify, enlarge or magnify the appearance ofmotion to make it more discernible to the user. In some cases, if therotation occurs at a constant rate, a timed pulse may be substituted asan input.

Another example may be a fan blade that comes back to the same positionin each rotation. As one example, using similar principles as describedfor a shaft, one of the fan blades may be marked as described herein(e.g., reflective tape) so that as the laser tachometer senses thatblade arriving at the original position, it will prompt the camera toobtain a series of images with the blade in the same orientation eachtime.

Techniques such as amplifying the motion may be employed to visualizeall the motion present that is due to the components not coming back totheir original locations. This will help visualize all nonsynchronousmotion such as torsional measurements on a shaft or fan bladevibrations. Additionally, measurements of motions may be made with fromthe video imagery frame to frame to demonstrate motion that isnonsynchronous. It will be appreciated that any number of measurementmethods may be employed, example include but are not limited to, edgetracking, feature tracking, template matching, or optical flow. In thesituation of a rotating shaft, for example, two measurements atdifferent locations on the shaft may not be the same. One location mayovershoot the equilibrium position while another may undershoot. Thisdelta will give the torsional variation of the shaft.

An external trigger in the form of a timed pulse may also be used tooffer a slightly detuned value of the shaft, resulting in the camerafiring off at a slightly different phase per revolution giving theeffect of making the rotating object seem to rotate slowly. At thispoint, software providing machine-readable program instructions may beused to make a high resolution (in-phase) measurement of the rotatingobject and apply techniques such as MOTION AMPLIFICATION® for a bettervisualization of the rotating component. An exemplary system and methodfor providing such enhancements is set forth in US Pub. No.2016/0300341, previously identified herein and incorporated byreference.

It will be appreciated that any number of external devices may be usedas a triggering device that trigger at a particular phase of the shaftor blade rotation, examples include, but are not necessarily limited to,optical sensors, proximity sensors, or high-speed cameras.

A motor turning at a rate of 1800 rpm or 30 Hz will serve as an example.The speed and frequency means the shaft will return to its originalposition 30 times in 1 second. Many conventional cameras, other thanones whose cost is much greater and potentially prohibitive, do not havethe precision to accurately synchronize with this rotation. A commonmethod of determining accurate position on a shaft is with a lasertachometer or photo tachometer. These devices are configured to sense adiscontinuity of the received signal. For example, in a machine having arotating shaft with a keyway formed in the surface of the shaft, a lasertachometer may be pointed at the shaft and each time the keywayinterrupts the signal, the laser tachometer senses this and sends apulse indicating that position on the shaft has returned to the samespot. Another optional approach is to place reflective tape on the shaftso that the laser can sense the change in signal due to the tapereflecting more signal. In other example use cases, known areascontaining non-uniformities on the shaft may produce such a change insignal sufficient to trigger an optical or proximity sensor. The resultis a pulsed signal that always triggers exactly at the same physicallocation on the shaft during each revolution. If one key way or piece ofreflective tape is used, then this occurs once per revolution.Alternatively, if more than one piece of reflective tape is used, thenthe signal is sent from the laser tachometer each time the reflectivetape passes under the laser beam.

Another way of triggering the once per revolution or N position eventsof a shaft may be by the use of a camera itself. If the camera isoperated at a high frame rate and sends an external trigger to one ormore other cameras when a certain pixel or set of pixels senses a changein signal, the camera could effectively be used as a trigger.

Still another example would be a photodiode or set of photodiodes set totrigger when they sense a change in the light level due to reflectivetape, keyways or some other discontinuities on the shaft.

The teachings herein can also be used to assess the motion of a fanblade. A laser tachometer or photo tachometer are examples of externaltriggers used to sense the return of a fan blade to its same position.In this case a piece of reflective tape 120 may be positioned on one ormore blades, such as shown in FIG. 12, such that the tachometer,photodiode, camera, or other sensing device senses the change in signalwhen the reflective tape comes into view of the triggering device. Inthis situation the result would be a signal generated every time theblade or blades return to the original position.

In a system in accordance with present embodiments that is configured toenlarge, amplify, or magnify the appearance of machine vibrations andmovement, videos are recorded at the shaft or fan blade being at thesame rotational position during each frame. Again, this arrangementallows all motions that do not return to a precise exact location ateach revolution to be detected and visualized. Examples of suchanomalous motion may be blade flutter, torsional vibration in a shaft orany other nonsynchronous motion.

Optical displacement measurements may also be made to quantify thesemovements. As desired, data may also be filtered to show individual orbands of frequencies of vibrations U.S. application Ser. No. 16/009,749,“Monitoring of objects based on frequency spectrum of motion andfrequency filtering” filed Jun. 15, 2018, describes such a filteringregimen. The entire contents of application Ser. No. 16/009,749, arefully incorporated by reference herein. Applying these techniques,frequencies of interest can be made to appear in the spectral data, butwith aliased frequency(-ies) values.

This may also be applied to non-rotating pieces of equipment, such asbut not limited to reciprocating equipment. Each time the reciprocatingcomponent comes back to the original position the camera may trigger tocapture an image essentially freezing the motion, Visualization tools toamplify or enlarge the appearance of motion in the video would now showall motions nonsynchronous to the reciprocating component.

Another illustrative instance of use may be to create N separate videoswhere N matches the number of fan blades, each marked with reflectivetape, where each video is created from frames where a blade is at thesame position each time. As one example, if a fan has 5 blades such asdepicted in FIG. 12, 5 videos would be created where each time the firstvideo has blade 1 at 0 degrees phase (i.e., equilibrium), the secondvideo has blade 2 at 0 degrees phase each time and so o.

A tachometer or similar device that sends a signal once per revolutionor when a particular feature comes into view will trigger an event suchas firing a camera when the rotating equipment reaches the exactlocation in rotation each time. an alternative scenario is using atiming device to trigger a camera. In this situation the shaft rotationspeed can be input into the timing device. The device would then pulseor trigger at the exact same rate with the rotation essentiallytriggering the camera each time the shaft reaches the same orientation.In this situation the shaft would need to be at the exact rate as theexternal triggering device.

In another alternative embodiment, the external triggering device may beadjusted to be slightly detuned from the shaft. For example, if theshaft is rotating at 30 Hz and the external trigger is set to 30.1 Hz,the result is the shaft will appear to move at 0.1 Hz, due to the factthat when the shaft comes back around, instead of triggering at 1/30 ofa second later, the camera triggers 1/30.1 seconds later orapproximately 0.00011 seconds later, allowing the shaft to rotateslightly more than 1 rotation. Accordingly, it will be appreciated thatdetuning the camera acquisition rate slightly off the rate of the camerato get a higher apparent rate of capture on the shaft could offersubstantially similar functionality as a high-speed camera. This canhave the benefit of applying techniques to amplify, enlarge or magnifythe appearance of motion due to the fact that the shaft appears to beonly slightly moving so there may be less smearing in the video andappear more fluid. It also can help in making optical displacementreading on the shaft since features in the shaft which are visiblelonger do not move as far and move slower making tracking easier to do.It further will be appreciated that the external clock could besubstituted for an internal clock in the camera in various embodimentsherein.

A specific case of measurement may be for the purpose of measuringtorsional motions on a shaft. In this example the laser tachometer orother rotational tracking device may be used. The laser tachometer wouldbe attached to the camera in such a manner that the laser triggers acamera acquisition exactly once per revolutions. Reflective tape or akeyway may be used to precisely trigger the camera such that the shaftis in the exact same position each time. The camera would be turned onand await a signal from the tachometer to begin acquiring frames. Thetachometer would be positioned at the shaft and trigger each time thereflective tape passes under the laser beam. A series of images would beacquired of the shaft at the exact same location. Even though thetachometer triggers the camera to take a picture of the shaft at thesame location each time as the reflective tape reaches the samelocation, still there will be other areas of the shaft whose locationmay vary relative to the location of the tape from one time to the nexttime the tape passes and triggers the camera.

Stated differently, and by way of examples with respect to the numbersused, if the reflective tape is considered to reach the laser tachometerat a phase angle of 10 degrees, an area to the right of the shaft, andaligned in its position at the same angle as the reflective tape whenthe shaft is stationary, may be at 11 degrees and such an area to theleft may be at 9 degrees while in operation. Then in the next frame anarea considered to be at the same angle as the reflective tape when theshaft is stationary to the right of the shaft may be at 9 degrees and anarea to the left at 11 degrees. This observation indicates that theshaft likely is undergoing torsional vibration.

In an exemplary use, markers are placed upon the right side and the leftside of a horizontally oriented shaft. As shown in FIG. 11, the markersare respective setscrews positioned on the right (110) and left (112) ofthe coupling, which is oriented so the shaft remains horizontal while itrotates. Alternatively, if the shaft were oriented so it remainsvertical while it rotates, the markers would be positioned relative totop and bottom areas of the coupling. Alternatively, as shown in FIG.10, one marker such as reflective tape 100 is positioned on a shaftlengthwise. The setup described here allows for the locations to bemeasured through the video to create a waveform of their verticalmovement. These waveforms can be compared to see variation to determinethe difference which indicates how much more or less once area of theshaft is moving in terms of rotation. A Fourier transform or similarprocess can be performed on the waveforms to determine the frequency. Adelta of the two waveforms can be used to determine the amount oftorsional motions. The parameters of the shaft such as radius materialand length could then be used to determine strain or stress on theshaft.

The tachometer output could be connected to a phase lock loop circuit tocreate a multiple of a trigger frequency, such as 6×, that could be usedto trigger camera acquisition and track the rotation during transientconditions, such as a period when the speed is varying. Despite the factthat the shaft speed is changing, it will trigger the camera six timesper revolution, thus capturing six images in the video per revolutionthroughout the transient conditions. Time synchronous averaging couldthen be applied to the images by co-adding the same indexed frame ofeach video to eliminate noise and show only synchronous motion relatedto the rotation event.

The tachometer may also be used to track the rotation during a coastdown or start up. Despite the fact that the shaft speed is changing itwill trigger the camera when the shaft reaches the same rotationalorientation creating one image in the video per revolution through anentire startup or coast down. The result will be all the motion presentfrom components not returning to the original positions. Transients andexcessive vibrations at particular frequencies or due to a particularturning speed will easily be seen especially when processes through amotion amplification technique. Rotational speed may be tracked throughtiming of the frames or other external methods such as other speedsensors, to correlate the instantaneous rotational speed to the acquiredframes such that the motions measured and visualized in the triggeredvideo frames can be determined to be occurring at specific turningspeeds.

Another technique may be to trigger only the initial frame with anexternal trigger and then record at a set frame rate after the initialframe. This would allow for the use of an impact hammer or modal hammerto initiate data acquisition. The resulting data could then becorrelated with the input data. A series of videos could be created thisway, all starting for example at the time of impact of an object or whenthe shaft is at a particular phase. Averaging data from sets of imagesacquired due to triggers from repetitive impacting events could thenfacilitate identification of resonant frequencies in the structure beingobserved. Negative averaging of such data can be applied so that impacttest can be performed on an operating machine. The machine is impactedmultiple times as described above and the averaged frequency spectrum iscalculated, Subsequent data is acquired with no impacting occurred andthese averages are subtracted from the averaged impact frequencyspectrum. The data in any frequency bin is not allowed to go below zeroand the negative averaging continues until the lines in the spectrumassociated with normal operation of the machine have been reducedsignificantly or to zero. The result of negative averaging is to removepeaks related to the normal operation revealing the peaks which are dueto resonant frequencies in the structure excited by the impacts to thestructure.

Still further, in another instance, multiple marks may be placed on theshaft. By way of example, again consider four marks equally placed asrepresented schematically in FIG. 13A, and their change in positioningas represented in FIGS. 13B and 13C when the shaft is rotating.Initially, only two marks are visible at a given time. For marks 1 and2, as indicated in FIG. 13B, mark 1 is near the top of the shaft as seenby the camera. The system may track mark 1 as it moves down the shaftduring rotation in order to measure how far it moved during each frame.Then as mark 1 is about to leave the field of view, the system may beginto track mark 4 as shown in FIG. 13C. When mark 4 is about to leave thefield of view it may begin to track mark 3. When mark 3 is about toleave the field of view it may begin to track mark 2. In this way themeasurements can be stitched together to create an accurate path for theentire rotation. By knowing the radius of the shaft it will beappreciated that the apparent displacement of the marks can betranslated to angular motion. The process can be repeated and switchedtogether to create a waveform showing the angular motion over time ofthe shaft for measurements of torsion or other shaft abnormalities.

Thus, in FIGS. 13A-C, a series of marks, which could be reflective tapeplacements on the unit shown in FIG. 10 or 11, for example, are depictedand a change in the positioning of the marks based on the component'smotion, is indicated. As indicated, this is done in order to compare forvariations along the shaft, in which the delta between measuredwaveforms is associated with a variation in angular motion along thelength of the shaft. FIG. 13B represents the shaft at a time designatedas “A” in the figure, where four marks equally spaced around the shaftare at a given orientation relative to the shaft. The mark labeled “1”may be considered the given or equilibrium orientation, while mark “2”is at another orientation and also visible to the camera at this point.Later, at a time designated as “B” in FIG. 13C, the shaft has rotatedsuch that mark “1” has moved to the bottom, and now mark “4” (not seenin the previous frame) has come into view. Conversely, in FIG. 13C,corresponding to time “B,” the marks “2” and “3” are on the backside ofthe shaft and not visible to the camera at this point.

In FIGS. 13A-C, the series of marks is four in number, but a differentnumber than 4 marks can be used as well. Many marks can be helpful suchthat switching between marks is made more frequently and closer to theposition of the shaft closest to the camera. This would provide a moreaccurate measurement as the apparent vertical motion would be greatestand less affected by the curvature of the shaft.

In some embodiments, various options exist to account for bulk motion ofa rotating component such as a shaft, to avoid a situation wherenon-torsional or non-rotational motion mimics torsional or shaftrotation. For example, an edge (top or bottom or both) of the shaft maybe measured and the up and down motion of the entire shaft accountedfor. The system may subtract off this motion such that any motionmeasured by the marks on the shaft has the bulk motion of the shaftremoved. The shaft may rock also so multiple measurements along thelength of the shaft on the edge may be made. An angle of the shaftrocking may be made this way and the rocking motion of the shaft mayalso be removed from the measurement of the motion of the markings. Asdesired or needed, various techniques may be employed to facilitatethese adjustments, including optical flow, template matching, lineprofiling, edge detection, and others.

It will be understood that the embodiments described herein are notlimited in their application to the details of the teachings anddescriptions set forth, or as illustrated in the accompanying figures.Rather, it will be understood that the present embodiments andalternatives, as described and claimed herein, are capable of beingpracticed or carried out in various ways. Also, it is to be understoodthat words and phrases used herein are for the purpose of descriptionand should not be regarded as limiting. The use herein of such words andphrases as “including,” “such as,” “comprising,” “e.g.,” “containing,”or “having” and variations of those words is meant to encompass theitems listed thereafter, and equivalents of those, as well as additionalitems.

Accordingly, the foregoing descriptions of embodiments and alternativesare meant to illustrate, rather than to serve as limits on the scope ofwhat has been disclosed herein. The descriptions herein are not meant tolimit the understanding of the embodiments to the precise formsdisclosed. It will be understood by those having ordinary skill in theart that modifications and variations of these embodiments arereasonably possible in light of the above teachings and descriptions.

What is claimed is:
 1. A method for evaluating a moving objectundergoing periodic motion using at least one video acquisition devicethat acquires initial sampling data as a plurality of video images ofthe moving object which are divisible into individual video imageframes, and with each frame being divisible into a plurality of pixels,comprising: causing a change in motion of the moving object using anexternal trigger to initiate an origin frame recorded with the at leastone video acquisition device, wherein the origin frame represents one ofthe plurality of video images; correlating sampling data obtained afterthe change in motion of the moving object with the origin frame; andusing the correlated sampling data to create a video of the movingobject based on the initial sampling data.
 2. The method of claim 1,wherein the plurality of video images are in a sequence, and the originframe comes after a first of the plurality of video images in thesequence.